Soviet spymasters tried to force a top British scientist to defect at during the height of the Cold War, he revealed today.

Sir Bernard Lovell, the man behind the pioneering Jodrell Bank observatory, said he had acted as a secret adviser to the British military and was prevented from leaving the Soviet Union during a landmark visit in the 1960s.

And the 95-year-old revealed in an interview that he secretly modified the design of the iconic Lovell radio telescope at the Cheshire observatory to function as an early warning system for a ballistic missile attack.

The celebrated astronomer and physicist said he had to plead with his hosts to secure his safe return - and suffered from a strange and violent illness on his return.

He said: 'The evidence is that the Soviets did try to keep me in the Soviet Union. I was extremely ill when I came back.'

Asked if he believed he had been drugged or brainwashed, he would say only that his full account of the ordeal would be published after his death.

Sir Bernard was one of the first westerners to be shown the country's space facilities when he was a guest of the Soviet Academy of Science in June and July 1963.